Evolution of Oxide Inclusions in Si-Mn Killed Steels During Hot-Rolling Process
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ORD steel, typical of Si-Mn killed steels, is a raw material for the production of tire cords. A crucial issue of the steel is breakage during cold drawing and fabrication, mainly caused by nonmetallic inclusions. Much research[1–9] on controlling the cleanliness and inclusions of tire-cord steel through adjusting the top refining slag have been performed either experimentally or via thermodynamic predictions, focusing on the precasting process rather than on rolling. Commonly, inclusions in tire-cord steel are classified as belonging to the SiO2-MnO-Al2O3 system or the SiO2-CaO-Al2O3
WEN YANG and LIFENG ZHANG are with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing (USTB), Beijing 100083, China. Contact email: [email protected] CHANGBO GUO is with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing (USTB), and also with Qingdao Iron and Steel Group Co., Ltd., Qingdao 266000, China. HAITAO LING is with the School of Metallurgy Engineering, Anhui University of Technology, Ma’anshan 243002, Anhui, China. CHAO LI is with the R&D Institute, HBIS Group Co., Ltd., Shijiazhuang 050023, Hebei, China. Manuscript submitted December 16, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
system. Within the same system, specific inclusions may be drastically different. The different melting points and plasticity cause different effects on the steel properties. Although breakages occur in cold-drawn wires, the inclusions are acquired during hot rolling. Steel wire rods for cold drawing are usually rolled from the billet by four hot-rolling passes. By more completely understanding the behavior of different inclusions during hot rolling, the operations of steelmaking and refining could be performed more appropriately to improve the properties of the wires and the final product. Many theoretical works[10–19] and experimental investigations[20–43] have been presented on the behaviors of inclusions during hot rolling. Theoretical works are generally performed using the finite element method (FEM). Stresses and strains in and around inclusions are well represented by FEM simulations. However, many assumptions are incorporated in such numerical analyses. In addition, because of limited computing ability, it is difficult to calculate cases with extremely large compression ratios and composite inclusions. Thus, it is difficult to accurately simulate the inclusion behaviors in an industrial hot-rolling process. Experimental investigations have mainly focused on determining the plasticity of inclusions by measuring their dimensions after rolling, as well as the formation of surrounding voids. Different inclusions, including sulfide, silicate,
Table I.
Slag Compositions of Experimental Heats (Weight Percent)
Compound
CaO
SiO2
Al2O3
MgO
FeO
MnO
CaF2
Basicity
Heat 1 Heat 2
57.98 30.14
27.61 37.30
1.47 1.69
3.32 9.39
0.54 17.56
0.07 3.92
9.01 —
2.10 0.81
and aluminate, have been studied. However, in previous investigations, usually o
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